Mapping the Great Indoors

On a sunny Wednesday, with a faint haze hanging over the Rockies, Noah Fierer eyed the field site from the back of his colleague’s Ford Explorer. Two blocks east of a strip mall in Longmont, one of the world’s last underexplored ecosystems had come into view: a sandstone-colored ranch house, code-named Q. A pair of dogs barked in the backyard.

Dr. Fierer, 39, a microbiologist at the University of Colorado Boulder and self-described “natural historian of cooties,” walked across the front lawn and into the house, joining a team of researchers inside. One swabbed surfaces with sterile cotton swabs. Others logged the findings from two humming air samplers: clothing fibers, dog hair, skin flakes, particulate matter and microbial life.